This is a renewal application to permit us to continue studies intended to develop in inbred Syrian hamsters a model of human urinary bladder cancer. The work so far carried out confirms Saffiotti's observations that beta-naphthylamine and o-amino-azotoluene do induce bladder cancer in Syrian hamsters. The hyperplastic changes in the bladder epithelium of hamsters treated for relatively short periods with the carcinogens suggest that a significant incidence of cancers is to be expected and that, therefore, it is worthwhile to continue the study and to extend it to include hitherto untested inbred lines.